CLIPS

CLIPS, short for C Language Integrated Production System, is a public domain software tool for building expert systems, programs that encode specialist knowledge as rules. Its syntax and name were inspired by Charles Forgy's OPS, the Official Production System, although nothing about that earlier system was really official. The first versions of CLIPS were developed starting in 1985 at NASA Johnson Space Center, as an alternative to the existing ART*Inference system, and work continued there until the mid-1990s, when the development group's responsibilities ceased to focus on expert system technology. Rosetta Code carries snippets in CLIPS, the History of Programming Languages register lists it, and thousands of public repositories on GitHub use it.